Anisotropic cosmological models in f(R,T) gravity according to holographic and new agegraphic dark energy

The paper deals with a spatially homogeneous and anisotropic universe filled with perfect fluid and dark energy components. We consider the f(R,T) theory according to holographic and new agegraphic dark energy in the Bianchi type I universe. In this study, we concentrate on two particular models of f(R,T) gravity namely, R+2f(T) and f(R)+λT. We conclude that the derived f(R,T) models can represent phantom or quintessence regimes of the universe.     

Cosmological evolution for dark energy models in f(T) gravity

In this paper, we investigate the behavior of equation of state parameter and energy density for dark energy in the framework of f(T) gravity. For this purpose, we use anisotropic LRS Bianchi type I universe model. The behavior of accelerating universe is discussed for some well-known f(T) models. It is found that the universe takes a transition between phantom and non-phantom phases for f(T) models except exponential and logarithmic models. We conclude that our results are relativity analogous to the results of FRW universe.     

Holographic f(T) gravity model

We try to study the corresponding relation between f(T) gravity and holographic dark energy (HDE). A kind of energy density from f(T) is introduced which has the same role as HDE density. A f(T) model according to the HDE model is calculated. We find out a torsion scalar T based on the scalar factor is assumed by Capoziello et al. (Phys. Lett. B 639:135, 2006). The effective torsion equation of state, deceleration parameter of the holographic f(T)-gravity model are calculated.     

Cosmic acceleration and phantom crossing in f(T)-gravity

In this paper, we propose two new models in f(T) gravity to realize universe acceleration and phantom crossing due to dark torsion in the formalism. The model parameters are constrained and the observational test are discussed. The best fit results favors an accelerating universe with possible phantom crossing in the near past or future followed respectively by matter and radiation dominated era.     

Cosmology from induced matter model applied to 5D f(R,T) theory

It is well known that the universe is undergoing a phase of accelerated expansion. Plenty of models have already been created with the purpose of describing what causes this non-expected cosmic feature. Among them, one could quote the extradimensional and the f(R,T) gravity models. In this work, in the scope of unifying Kaluza-Klein extradimensional model with f(R,T) gravity, cosmological solutions for density and pressure of the universe are obtained from the induced matter model application. Particular solutions for vacuum quantum energy and radiation are also shown.     

Effective dark energy models and dark energy models with bounce in frames of F(T) gravity

Various cosmological models in frames of F(T) gravity are considered. The general scheme of constructing effective dark energy models with various evolution is presented. It is showed that these models in principle are compatible with ΛCDM model. The dynamics of universe governed by F(T) gravity can mimics ΛCDM evolution in past but declines from it in a future. We also construct some dark energy models with the “real” (non-effective) equation-of-state parameter w such that w≤?1. It is showed that in F(T) gravity the Universe filled phantom field not necessarily ends its existence in singularity. There are two possible mechanisms permitting the final singularity. Firstly due to the nonlinear dependence between energy density and H ² (H is the Hubble parameter) the universe can expands not so fast as in the general relativity and in fact Little Rip regime take place instead Big Rip. We also considered the models with possible bounce in future. In these models the universe expansion can mimics the dynamics with future singularity but due to bounce in future universe begin contracts.     

Generalized teleparallel gravity via some scalar field dark energy models

We consider generalized teleparallel gravity in the flat FRW universe with a viable power-law f(T) model. We construct its equation of state and deceleration parameters which give accelerated expansion of the universe in quintessence era for the obtained scale factor. Further, we develop correspondence of f(T) model with scalar field models such as, quintessence, tachyon, K-essence and dilaton. The dynamics of scalar field as well as scalar potential of these models indicate the expansion of the universe with acceleration in the f(T) gravity scenario.     

Generalized second law of thermodynamics in QCD ghost f(G) gravity

Considering power-law for of scale factor in a flat FRW universe we reported a reconstruction scheme for f(G) gravity based on QCD ghost dark energy. We reconstructed the effective equation of state parameter and observed “quintessence” behavior of the equation of state parameter. Furthermore, considering dynamical apparent horizon as the enveloping horizon of the universe we have observed that the generalized second law of thermodynamics is valid for this reconstructed f(G) gravity.     

Reconstruction of f(R), f(T) and f(\mathcal{G}) models inspired by variable deceleration parameter

We study an special law for the deceleration parameter, recently proposed by Akarsu and Dereli, in the context of f(R), f(T) and $f(\mathcal{G})$ theories of modified gravity. This law covers the law of Berman for obtaining exact cosmological models to account for the current acceleration of the universe, and also gives the opportunity to generalize many of the dark energy models having better consistency with the cosmological observations. Our aim is to reconstruct the f(R), f(T) and $f(\mathcal{G})$ models inspired by this law of variable deceleration parameter. Such models may then exhibit better consistency with the cosmological observations.     

Bulk viscous cosmological models in f(R,T) theory of gravity

We have constructed Locally Rotationally Symmetric Bianchi type I (LRSBI) cosmological models in the f(R,T) theory of gravity when the source of gravitation is the bulk viscous fluid. The models are constructed for f(R,T)=R+2f(T) and f(R,T)=f ₁(R)+f ₂(T). We found that in the first case the model degenerates into effective stiff fluid model of the universe. In the second case we obtained degenerate effective stiff fluid model as well as general bulk viscous models of the universe. Some physical and kinematical properties of the models are also discussed.     

Reconstruction of f(R,T) gravity in anisotropic cosmological models of accelerating universe

In this paper, we search the existence of Bianchi type I cosmological model in f(R,T) gravity, where the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar R and of the trace of the stress-energy tensor T. We obtain the gravitational field equations in the metric formalism, and reconstruct the corresponding f(R,T) functions. Attention is attached to the special case, f(R,T)=f ₁(R)+f ₂(T) and two examples are assumed for this model. In the first example, we consider the unification of matter dominated and accelerated phases with f(R) gravity in anisotropic universe, and in the second instance, model of f(R,T) gravity with transition of matter dominated phase to the acceleration phase is obtained. In both cases, f(R,T) is proportional to a power of R with exponents depending on the input parameters.     

Reconstruction of f(T) gravity from the Holographic Dark Energy

Among different candidates to play the role of Dark Energy (DE), modified gravity has emerged as offering a possible unification of Dark Matter (DM) and DE. The purpose of this work is to develop a reconstruction scheme for the modified gravity with f(T) action using holographic energy density. In the framework of the said modified gravity we have considered the equation of state of the Holographic DE (HDE) density. Subsequently we have developed a reconstruction scheme for modified gravity with f(T) action. Finally we have obtained a modified gravity action consistent with the HDE scenario.     

New agegraphic dark energy in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) gravity

In this paper, we study a cosmological application of the new agegraphic dark energy density in the f(R) gravity framework. We employ the new agegraphic model of dark energy to obtain the equation of state for the new agegraphic energy density in a spatially flat universe. Our calculations show, taking n<0, that it is possible to have w _Λ crossing −1. This implies that one can generate a phantom-like equation of state from a new agegraphic dark energy model in a flat universe in the modified gravity cosmology framework. Also, we develop a reconstruction scheme for the modified gravity with f(R) action.     

Evolution of the universe in inverse and lnf(R) gravity

Evolution of the universe is discussed in the framework of f(R) theory of gravity. The deceleration parameter is used to interpret various phases of the universe. We investigate the future evolution of the flat FRW universe by using observationally viable f(R) models. A numerical technique is applied to solve the evolution equation in terms of Hubble parameter which is used to explore late time acceleration of the universe. Some novel and interesting results based on the choice of coupling parameters in gravitational action are obtained. We can conclude that the considered f(R) models imply unification of matter dominated epoch with present accelerating phase of the universe.     

A holographic reconstruction scheme for f(R) gravity and the study of stability and thermodynamic consequences

The present paper reports a study of the reconstruction of f(R) gravity from holographic Ricci dark energy, a specific case of Nojiri–Odintsov holographic DE (ref Nojiri and Odinstov, 2005a), in the presence of bulk viscosity. The reconstructed equation of state (EoS) parameter w_R was found to have a transition from quintessence to phantom in the absence of the bulk viscosity. Thus, the behaviour of w_R for this reconstruction scheme was identified as “quintom” in the absence of the bulk viscosity. However, in the case of the bulk viscous scenario w_R behaves like “quintessence”. Furthermore, the generalized second law of thermodynamics was tested in the case of the reconstructed f(R) gravity. Finally, the stability of this model against small perturbations was demonstrated with the aid of squared speed of sound.     

Pilgrim dark energy in f(T,T G ) cosmology

We work on the reconstruction scenario of pilgrim dark energy (PDE) in f(T,T _G ). In PDE model it is assumed that a repulsive force that is accelerating the Universe is phantom type with (w _DE f(T,T _G ) models and correspondingly evaluate equation of state parameter for various choices of scale factor. Also, we assume polynomial form of f(T,T _G ) in terms of cosmic time and reconstruct H and w _DE in this manner. Through discussion, it is concluded that PDE shows aggressive phantom-like behavior for s=?2 in f(T,T _G ) gravity.